1. Field of the Invention
The present invention relates to an apparatus and a method for feeding a sintering raw mix, and more particularly, it relates to an apparatus and a method for feeding a sintering raw mix to produce a sintered ore for feeding into a blast furnace.
2. Description of the Related Art
Conventionally, in the iron and steel industry, when a sintering ore is fed into a blast furnace, a sintering apparatus uses coke breeze having a grain size suitable for an iron ore powder with a wide range of grain sizes of from a few .mu.m to about 10 mm and an average diameter of 1 to 3 mm, and if necessary, burnt lime powders are mixed therewith, the mixture is fed onto a sintering pallet, the coke breeze in the surface raw mix layer is ignited to burn the coke while breathing air, and the fine ore is sintered by the burning heat.
Since, in this sintering apparatus, sintering is advanced by burning the coke breeze, the supply of air to the sintering layer, i.e., permeability, is very important for a sintering operation.
As a process for improving a permeability of a sintering raw mix layer, a pretreatment of a sintering raw mix itself (hereinafter referred to as a raw mix) is conventionally well known. In this pretreatment, various raw mixes to which a suitable amount of water has been added are mixed and granulated by a drum mixer so that large pseudo-particles having a larger grain size than the original grain size are produced. Further, in this pretreatment the addition of burnt lime to the raw mix to promote the production of pseudo-particles is also carried out. However, these improvements do not fully overcome the above-mentioned permeability problems.
On the other hand, when the above-mentioned pretreated raw mix is fed by a sloping chute which is usually provided at a sintering installation, a phenomenon occurs wherein the small size raw mix is stacked in the upper raw mix layer and the large size raw mix is stacked in the lower raw mix layer. Preferably, the pallet has percolation, i.e., a raw mix and coke grain size segregation occurs in the height direction of the raw mix layer, so that an improved heat pattern can be obtained. However, a slip phenomena often occurs when feeding the raw mix onto the pallet, and the above segregation is disturbed so that a part of both the fine ore and the coke breeze are mixed in the lower raw mix layer and a non-uniform structure with regard to grain size is formed. Consequently, an improved heat pattern cannot be obtained.
As a method for solving the above mentioned problem, a well known method of feeding a raw mix is disclosed in Japanese Unexamined Patent Publication (Kokai) No. 61-223136. This method, i.e., an intensified sifting and a grain-dispersion type feeding, is carried out, as shown in FIG. 1, by providing a number of bars or rods 2 about the pallet which forms a strand extending in a pallet advancing direction, in such a manner that the free ends of the bars are at different levels.
This feeding process will be explained in detail. First, a raw mix stored in a hopper 3 is fed rom a drum feeder 5 so that the raw mix falls on the bars 2 via a sloping plate 6. Since in this case the bars are sloped, and the pallet moves toward the free lower ends of the bars, so that the forward end of the pallet 1 receives the lower portion of the layer and the free end portions of the bars 2 are at different levels, the gaps between the bars are wider at the free ends. Thus, fine particles of the raw mix falling on the bars 2 fall through to the pallet 1 from ends toward the pallet, and coarse particles of the sintering raw mix fall through to the pallet 1 from the free ends of the bars 2, whereby a sift feeding to form a lower coarse particle layer and an upper fine particle layer on the pallet is carried out so that a grain size in the height direction of a raw mix layer can be optionally formed. Since, in this type of feeding, when the raw mix falls it is widely dispersed in the strand direction, the slip which occurs in the chute type is avoided, and the filling structure of the raw mix becomes uniform, and as a result, a uniform heat in the height direction of the bed can be realized. Further, in the feeding, by a sizing due to sifting and by the falling energy reduction due to collision with the bars during the falling of the raw mix, a low density feeding is carried out, and thus a high permeability can be obtained. However, since water is contained in a raw mix which is fed into a sintering apparatus to produce pseudo-particles from a fine raw mix, the raw mix will easily adhere to the bars, and when a burnt lime is used in the raw mix, the degree of adherence becomes large.
Further, since the gaps between the bars 2 are 5 to 30 mm, which is very small, when the sintering raw mix adheres to the bars 2, the gap between the bars 2 is narrowed, and thus the sifting and the grain-dispersion of the raw mix are not efficiently carried out. When the adhered layer on the bars 2 becomes too thick, the bars 2 cease to function as a screen. Further, since the sintering raw mix falling from the sloping plate impinges constantly upon the same portions of the bars 2, local wear is generated on the bars 2.
Thus, conventionally, the operation of the sintering apparatus must be periodically stopped to remove the adhered raw mix and replace worn bars 2. However, since this removal and replacement must be carried out in a narrow space, it is very cumbersome, and undue wastage of the bars 2 occurs because the entire body of each bar 2 is discarded although there is local wear on only portions thereof.
Japanese Examined Patent Publication (Kokoku) filed on Oct. 31, 1966) discloses a screen apparatus for sifting particles, in which a number of bars are arranged so that two adjoining bars have a different slope, and particles are sifted by oscillating these bars. Even in such a process, wherein particles are sifted while oscillating the bars, although a slight improvement is attained due to a difference in the oscillating frequency, the adhesion of particles to the bars cannot be completely eliminated.
Further, two Japanese Utility Model applications (Nos. 62-18098 and 62-29249) concerning an apparatus for removing adhered particles to bars, were filed on Jan. 10, 1987. The apparatus of JUM-098 as shown in FIG. 2 is constructed in such a manner that counterweights 9a and 9b arranged at the bar base end portion are struck by a hammer 12 having a hammer lever 10 and an oscillating arm 11, so that an impact force is given to bars 2, to separate and remove particles adhered to the bars 2. In FIG. 2 14a and 14b are cylinders.
However, in the process using the apparatus of JUM-098, the adhered particles are only substantially, not completely, removed. After a short time, e.g., about 10 sec, the usual adhered state is again encountered. This state is shown in FIG. 3A (side view) and FIG. 3B (plane view). From FIGS. 3A and 3B, it can be seen that a large amount of the sintering raw mix 15 is adhered to the bars 2.
The apparatus of JUM-249, as shown in FIG. 4, is constructed in such a manner that, by reciprocating a cleaner 19 formed by scrapers 17 and chips 18, a sintering raw mix adhered to bars is removed. In FIG. 4, 20 is a carriage for carrying the cleaner 19, which is moved along a guide rail 21, and 14a and 14b are cylinders.
In the process of JUM-249, the raw mix adhered to the bars is substantially removed, as in the process disclosed in JUM-098, but if the gaps between the bars are filled by the raw mix for only about ten sec, the usual adhered state is again encountered. This state is shown in FIG. 5A (side view) and FIG. 5B (plan view). As shown in FIGS. 5A and 5B the amount of raw mix 15 adhered to the bar 2 is high, as in the case where the adhered raw mix is not removed by the above-mentioned cleaners.